In the automatic transmission prior art, particularly for motor vehicles, transmissions comprise planetary gear sets which are shifted by means of friction or shifting elements, such as clutches and brakes, and are usually connected with a starting element, such as a hydrodynamic torque converter or a fluid clutch, subject to a slip effect and optionally provided with a lock-up clutch.
Such a transmission results from EP 0 434 525 A1. It essentially comprises one drive shaft and one driven shaft disposed parallel with each other, one double planetary gear set disposed concentrically to the driven shaft and five shifting elements in the form of three clutches and two brakes, the optional locking of which by pairs determines the different gear ratios between the drive shaft and the driven shaft. This transmission has one planetary reduction gear set and two power paths so that by selective engagement by pairs of the five shifting elements six forward gears are obtained.
In the first power path are needed two clutches for transmitting the torque from the planetary reduction gear set to two elements of the double planetary gear set. These are disposed, axially observed, essentially behind the reduction gear set in direction of the double planetary gear set. In the second power path is provided one other clutch which loosely connects it with one other element of the double planetary gear set. The clutches are arranged here in a manner such that the internal disc carrier constitutes the output.
From the published U.S. Pat. No. 6,139,463 is further known a multi-stage transmission in planetary design, specially for a motor vehicle, which has two planetary gear sets and one planetary reduction gear set, the same as three clutches and two brakes. In this already known multi-stage transmission, two clutches C-1 and C-3 are provided in the first power path for transmitting the torque from the planetary reduction gear set to the two planetary gear sets. The external disc carrier or the cylinder or piston and pressure compensation side of the clutch C-3 is connected with a first brake B-1. Besides, the internal disc carrier of the third clutch C-3 is connected with the cylinder or piston and pressure compensation side of the first clutch C-1, the internal disc carrier of the first clutch C-1 being situated on the output side and connected with a sun gear of the third planetary gear set.
The known multi-stage transmission has the disadvantage that, particularly in the sixth gear, the first brake B-1 is closed. Thereby stands the cylinder of the third clutch C-3 so that no hydrodynamic pressure can build up. In this manner, the pressure compensation space of the third clutch can run idle whereby the shifting quality of the known multi-stage transmission is impaired.
From the published U.S. Pat. No. 6,135,912 is further known a similar multi-stage transmission. In this multi-stage transmission which, likewise, has two clutches C-1 and C-3 for transmitting the torque from the planetary reduction gear set to the planetary gear sets, the internal disc carriers of these clutches are preferably connected with the planetary gear sets. One other embodiment disclosed within the scope of the cited publication provides that the external disc carrier of the clutch C-3 is situated on the output side. This construction, specially the arrangement of the clutches relative to the output or input, has also been disclosed within the scope of U.S. Pat. No. 6,120,410 which also describes a multi-stage transmission of the type mentioned.
The problem on which this invention is based is to propose a multi-stage transmission of the above mentioned type in which the shifting quality is improved. A clutch system is to be specially indicated which, in compact design, makes it possible to implement a quick and comfortable shifting behavior.